update contributing guide with clear test deps

CONTRIBUTING.md

@@ -3,7 +3,20 @@
 Patches are welcome! Please use the standard GitHub workflow - fork this
 repo and submit a PR. I'll usually get to it within a few days.
 
-Handy commands for local development:
+## Setting up dev environment
+
+- Install [Goland](https://www.jetbrains.com/go/), [Atom](https://atom.io/),
+or your favorite web editor with Golang support.
+
+```
+cd $GOPATH/src/github.com/issmirnov/zap
+go build . # sanity check
+
+# install test deps
+go get github.com/smartystreets/goconvey
+```
+
+## Handy commands for local development:
 
 - `go run main.go config.go text.go web.go` to run locally
 - `curl -I -L -H 'Host: g' localhost:8927/z` - to test locally e2e